I cannot put any weight on my knees. Are there any exercises I can do without getting down to floor level? I have osteoarthritis.

The most obvious options are low impact activities such as walking (especially on flat ground!), golf or maybe even a bit of dance! YouTube is a great source here and you can always adapt specific movements to something you are comfortable with. Additionally, you may want to try cycling and swimming as these activities are also pretty low in terms of intensity and avoid putting any impact on the joints.

If these don't suit, your GP may be able to advise on specific exercise classes for your condition. If these aren't able to go ahead in person at the moment, many will offer an online alternative.